The 2012 status of the MCAO testbed for the GREGOR solar telescope

摘要

We look back on two years of experience with the laboratory MCAO testbed for the GREGOR solar telescope.GREGOR’s MCAO features four adaptive mirrors, i. e. one tip-tilt mirror, and three DMs to compensate forturbulence around 0 km, 5 km, and 15.5 km above ground. Two different Hartmann-Shack wavefront sensor unitsare used for wavefront tomography. A sensor with a narrow field of view and smaller subapertures is dedicated tohigh-order aberrations on the optical axis. This sensor directly follows the pupil plane DM and does not see thehigh-altitude DMs. The second sensor features larger subapertures and 19 guide regions spread over a wide fieldof view for off-axis wavefront sensing. We show that high-altitude DMs cause rapidly changing pupil distortionsand thus misregistration, which renders the interaction of a pupil-plane DM and a subsequent wavefront sensornon-linear.We rewrote the control software for cleaner and more flexible code, and we switched to modal wavefrontreconstruction from direct reconstruction. The original digital interfacing of the DMs high-voltage electronicsdidn’t prove to be reliable. Thus, we developed a new interface board that is based on CameraLink/ChannelLinktechnology to transmit the DM commands from the control computer.In this paper we present the innovations and some of the first experimental performance measurements withtwo DMs. One DM failed before scientific grade data was recorded with three DMs. This DM will be replacedsoon. We conclude that GREGOR’s MCAO system is now ready for first on-sky tests at the telescope.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.